Carbon monoxide is usually obtained by separation from synthesis gases produced by catalytic conversion or partial oxidation of natural gas, oils or other hydrocarbon feedstock. In addition to carbon monoxide, these gases contain primarily hydrogen and methane but are often contaminated with significant amounts of nitrogen (derived from the feed or added during processing). Conventional cryogenic separation processing leaves nitrogen as an impurity in the carbon monoxide, which, for both environmental and processing reasons, is unacceptable for some uses of carbon monoxide. The problem of nitrogen contamination of carbon monoxide product is becoming an increasing problem with the usage of more marginal feedstock in front end reforming processes. Further, there is an increasing demand for carbon monoxide to be free of argon, which sometimes is a co-contaminant with nitrogen. Accordingly, there is a demand for efficient and effective removal of contaminant nitrogen and, if required, argon from carbon monoxide-containing feeds.
The separation of nitrogen alone or with argon co-contaminant from carbon monoxide is relatively difficult compared to removal of hydrogen or methane. Prior art processes for removing nitrogen from synthesis gas usually include the sequential steps of removing hydrogen from the synthesis gas feed, removing methane from the resultant hydrogen-freed stream, and removing nitrogen from the resultant hydrogen- and methane-freed stream to leave a purified carbon monoxide product stream.
Related patents for producing carbon monoxide include U.S. Pat. Nos. 3,813,889, 4,217,759, 4,311,496, 4,478,621, 4,566,886, 4,888,035, 4,917,716 5,133,793, 5,295,356, 5,351,491, 5,351,492, 5,359,857, 5,509,271, 5,592,831, 5,609,040, 5,953,936, 6,073,461, 6,062,042, 6,070,430, 6,082,134, 6,094,938, 6,098,424, 6,173,585, 6,269,657, 6,467,306, 7,269,972, and German No. DE 195 41 339, all incorporated herein by reference.
It would be desirable to provide a more cost effective process for separating carbon monoxide from gaseous mixtures containing carbon monoxide, hydrogen, methane and nitrogen, especially those which also contain argon.